The present invention relates to the synthesis of ethanol from biomass and more particularly to a much improved synthesis by a catalytic thermochemical process.
Conversion of biomass to ethanol by fermentation techniques is a well practiced process, especially with the emerging importance of gasohol in today's economy. Conventional fermentation techniques, however, suffer from a number of drawbacks including, for example, protracted reaction times, the need for sterile reaction conditions, the need for purified feedstocks, the production of voluminous by-products, and an energy intensive distillation operation for recovery of ethanol from water. The need for an alternate route for converting biomass to ethanol thus exists. Unfortunately, no alternative process has emerged in the marketplace.
Related application U.S. Ser. No. 144,189 discloses a method for thermochemically converting a sacchariferous material into ethanol wherein a reaction mixture comprising water, said sacchariferous material, and a metallic salt is heated under reaction conditions of a temperature of between 150.degree. and 400.degree. C., a pressure of at least atmospheric, and for a time adequate for directly forming ethanol and a metallic oxide or hydroxide. The metal of the metallic salt is restricted to a metal whose metallic carbonate formed in the reaction zone decomposes under the reaction conditions to generate the metallic oxide or hydroxide in situ. Related application U.S. Ser. No. 144,190 discloses a method for making a liquid fuel-ethanol blend which comprises establishing an aqueous reaction mixture of the carbohydrate material, a metal salt, and water in a reaction zone held at elevated temperature of about 150.degree. C. to 300.degree. C. to form an intermediate carbohydrate complex of said metal and/or a metal lactate salt. The complex and/or lactate salt then is pyrolyzed at a temperature of about 275.degree. to 400.degree. C. in the presence of water in a pyrolysis zone to form ethanol. The ethanol is recovered and then blended with a combustible liquid fuel. Related application U.S. Ser. No. 144,194 discloses a method for making ethanol from a carbohydrate material wherein an aqueous reaction mixture of a carbohydrate material, water, and a metal salt are heated at elevated temperature to produce an intermediate complex and/or lactate salt which is separated from the reaction mixture. The separated complex and/or lactate salt and water then are admitted into a pyrolysis zone held at a temperature ranging from between about 250.degree. and 400.degree. C. to pyrolyze the complex and/or salt to form ethanol. The proportion of water in said zone is restricted to be not in substantial excess of that proportion required for formation of ethanol and by-product metallic carbonate.
While the foregoing thermochemical processes are a significant advance in the art, yields of ethanol generally are only a few percent of the theoretical proportion of ethanol that could be made. Thus, there is a need for improving the foregoing thermochemical processes so that the yields of ethanol are substantially increased. Moreover, the product mixture obtained by the above-described thermochemical processes contains many by-products in very minor proportions. Thus, there exists a need for suppressing by-product formation in such thermochemical processes. The present invention is addressed to solving these problems as well as providing numerous additional distinct advantages in the thermochemical process.